Underdrive pulleys slows down your alternator, A/C belts,etc. which makes your car go faster. There are several problems associated with this due to the electrical shortage it brings. And if you have a supercharger, you cannot replace these pulleys coz' superchargers are belt-driven and rely on the turns made by these pulleys.

: Has anyone heard any feedback on this new accessory from Turner Motorsport? They claim 9 hp gain with no negatives... Any thoughts?